Chemnitzer concertina/playing

The bass keyboard is less flexible than the treble.
Work out your bellows direction based on the needs of
the left hand first, and let that dictate right hand
fingering.

If you're playing chords in the left hand, you'll find
that in many keys (e.g. F, C, G, D, A, E), the tonic
and dominant work out easily in opposite bellows
directions; of course this was done on purpose for
folk music.

The bellows and air valve are critical. Learn to
anticipate bellows direction changes and as you
approach a change, slowly leak air through the valve
while playing so the bellows is positioned comfortably
for the next passage.

Depending on your style, some of this may not apply; for example,
Argentine Tango players play their bandoneóns almost
entirely on the draw of the bellows and use the air
valve to push out a big puff of air between passages.